Kennarinn krafði nemandann um svar.

The ending -inn is the definite article attached to the noun.

• kennari = teacher
• kennarinn = the teacher

In Icelandic, the definite article is usually added to the end of the noun instead of written as a separate word like English the.

So Kennarinn means the teacher, not just teacher.

Because nemandann is in the accusative case, while nemandinn would be nominative.

Here:

• kennarinn is the subject of the sentence, so it is nominative.
• nemandann is the person being demanded from / addressed by the action, so it appears in the accusative after krefja.

Compare:

• nemandinn = the student (nominative)
• nemandann = the student (accusative)

This is very common in Icelandic: the form of the noun changes depending on its role in the sentence.

The dictionary form is krefja.

In this sentence:

• krefja = to demand
• krafði = demanded (past tense, singular)

So Kennarinn krafði nemandann um svar means that the action happened in the past: the teacher demanded...

A learner may notice that krefja changes quite a lot in the past tense:

• infinitive: krefja
• past singular: krafði

That vowel change is just part of how this verb is formed.

Because this is a normal Icelandic main clause with standard word order:

Subject + Verb + Object + other parts

So:

• Kennarinn = subject
• krafði = verb
• nemandann = object
• um svar = prepositional phrase

This is very similar to ordinary English word order:

• The teacher demanded the student for an answer
  or more naturally in English,
• The teacher demanded an answer from the student

Icelandic can move words around more than English in some contexts, but this sentence uses a very straightforward order.

Here um means something like for in English.

So:

• krefja einhvern um eitthvað = to demand something from someone

In many other sentences, um often means about, around, or concerning, but after krefja it is part of the pattern of the verb.

So in this sentence:

• nemandann = the student
• um svar = for an answer

Together: demanded the student for an answer, which English normally expresses as demanded an answer from the student.

Because svar is indefinite here.

• svar = an answer / answer
• svarið = the answer

So the sentence means the teacher demanded an answer, not necessarily the answer.

If you said:

• Kennarinn krafði nemandann um svarið

that would mean The teacher demanded the answer from the student, referring to a specific answer.

It actually is in the accusative, but for this noun the nominative and accusative singular forms are the same.

• nominative: svar
• accusative: svar

This is very common with neuter nouns in Icelandic: nominative and accusative are often identical in the singular.

So after um, which here takes the accusative, the correct form is still simply svar.

The sentence contains two important cases:

• Kennarinn — nominative
  because it is the subject

• nemandann — accusative
  because krefja takes an accusative object

• svar — also accusative after um
  though its form looks the same as the nominative

So the structure is:

• subject in nominative
• object in accusative
• preposition um
  • accusative

Not exactly. They are related, but they are not used in quite the same way.

In your sentence, the verb is krefja:

• krefja einhvern um eitthvað
  = to demand something from someone

There is also krefjast, which learners often meet and confuse with it. That verb usually means to demand, to require, and it often has different grammar.

So it is worth learning this sentence pattern as a chunk:

• krefja + person (accusative) + um + thing

That will help you use this exact construction correctly.

Not very naturally.

A very literal breakdown would be:

• Kennarinn = the teacher
• krafði = demanded
• nemandann = the student
• um svar = for an answer

So a literal version would be:

The teacher demanded the student for an answer.

But natural English would usually be:

• The teacher demanded an answer from the student.
• or The teacher asked the student for an answer, depending on the intended tone

So even if the Icelandic structure is clear, you should not always expect the most natural English translation to match it word for word.

A very useful pattern is:

krefja einhvern um eitthvað

which means:

to demand something from someone

In this sentence:

• einhvern = nemandann
• eitthvað = svar

So you can use the same pattern with other words, for example:

• Hann krafði mig um skýringu.
  = He demanded an explanation from me.

• Lögreglan krafði manninn um skilríki.
  = The police demanded identification from the man.

Learning the whole pattern is often easier than trying to memorize each word separately.

You can tell from the noun’s dictionary form: kennari is a masculine noun.

That affects how the definite article and case endings work:

• kennari = teacher
• kennarinn = the teacher

Likewise, nemandi is also masculine:

• nemandi = student
• nemandinn = the student
• nemandann = the student (accusative)

So part of understanding the sentence is knowing the gender of the nouns, because Icelandic endings depend heavily on gender and case.

Yes. It is very typical Icelandic in several ways:

1. The definite article is attached to the noun

   • kennarinn, nemandann

2. Case marks grammatical role

   • subject in nominative, object in accusative

3. A verb can require a specific preposition

   • krefja ... um ...

4. The sentence can be more literal in Icelandic than in English
   even if natural English translation uses a different structure

So this one sentence gives you practice with several very important Icelandic features at once.